The present invention concerns an elastic bush including two rigid armatures which are coaxial when unstressed, namely an outer armature and an inner armature between which there extend, essentially in a radial direction, a set of elastic arms that in principle are equi-angularly distributed.
It can be used, for example, but not exclusively, to form the end of a torsion bar which is connected to the engine or to the bodyshell of a vehicle in which the engine is mounted transversely.
FIG. 1 of the accompanying drawings shows a prior art connecting bush for use in an application of the above kind in cross-section.
The figure shows a tubular outer armature 1xe2x80x2 and a tubular inner armature 2xe2x80x2 which are coaxial when unstressed. In this example an elastic connection is provided between the two armatures by four equi-angularly distributed natural or synthetic rubber arms 31 whose ends are bonded to the inner armature 2xe2x80x2 and to the inside face of the outer armature 1xe2x80x2. Part of the body C of a conventional torsion bar, for example for transversely mounted vehicle engines, is also shown.
When forces are applied to the bar axially, i.e. in the direction of the axis X, or when vertical forces are applied in the perpendicular direction represented by the axis Z, some of the arms 3xe2x80x2 are subjected to tensile stresses, which reduces the durability of the elastic bush. One attempt to remedy this provides a constriction on the outer armature 1xe2x80x2 to reduce the tension already present in the arms on removal from the mould, but the drawback referred to above remains.
The aim of the present invention is to remedy this drawback and to prevent the elastic arms from being stressed in tension during operation.
To this end, an elastic bush of the type mentioned above is characterised in that the elastic arms are bonded at their base to only one armature, their end opposite said base being between two adjoining rigid radial projections of the other armature.
As a result, forces acting in the directions X and Z (or the resultant of such forces) can stress each elastic arm only in compression, each elastic arm being guided and held between two adjoining rigid projections of the other armature. The arms opposite those on which compression forces are exerted are not subject to any force. They are subjected to compression forces only if the relative displacement of the two armatures is reversed and are never subjected to any tension force. There may be a clearance between said opposite end of each elastic arm and said other armature. If there is no such clearance, the arms are advantageously pre-stressed radially by compression of said opposite end against said other armature.
For good radial guidance of the elastic arms between the two adjoining rigid projections of the other armature it is possible for said rigid projections to have an enlarged free end, like the branches of a Maltese Cross, and for said elastic arms to have a cross-section that decreases in size from their base towards their opposite end, to impart to them the required elasticity as a function of the load.
To limit deformation of the bush under high loads the armature to which said elastic arms are bonded can have abutments between the arms facing the free ends of said rigid projections; for example, the armature to which said elastic arms are bonded can be bonded to an elastic material lining having radial extensions alternately constituting said elastic arms and said abutments, the abutments being significantly smaller in the radial direction than the elastic arms.
The abutments can have different thicknesses in the direction (X or Z) of the forces they are intended to withstand.
The elastic arms can in principle be bonded to the inner armature or to the outer armature but it is preferable for said arms to be bonded at their base only to the inside face of said outer armature, their end opposite said base extending between two adjoining rigid radial projections of the inner armature.